GCSE Astronomy — Exploring Starlight

Led by Annie Jump Cannon

About this course

The thirteenth module of the Edexcel GCSE Astronomy course is the spec's most data-dense unit. The student moves from the magnitude scale and the distance modulus through what stellar spectra reveal, the OBAFGKM classification scheme, the Hertzsprung-Russell diagram and stellar life cycles upon it, parallax and the parsec, and the variable-star families — eclipsing binaries, Cepheids, novae, and supernovae — that calibrate the cosmic distance ladder.

It is led by Annie Jump Cannon, who between 1911 and 1915 at the Harvard College Observatory classified more than 225,000 stellar spectra by hand and refined the temperature-ordered OBAFGKM sequence that remains the foundation of stellar spectral classification today.

The student leaves the module able to apply the magnitude scale and distance modulus, account for what stellar spectra reveal, classify by spectral type, sketch and use the Hertzsprung-Russell diagram, determine distances by parallax and spectroscopic parallax, and analyse the light curves of all the spec's required variable types.

1. Module 13

   Exploring Starlight

   Led by Annie Jump Cannon

   The question

   How is the brightness of a star measured, what does its spectrum reveal, how is it classified, where does it sit on the Hertzsprung-Russell diagram and what does its position there tell us about its life cycle, how is its distance determined by parallax or by spectroscopic methods, and what do the light curves of variable stars — eclipsing binaries, Cepheids, novae, supernovae — reveal? The spec asks for the magnitude scale, the distance modulus, the OBAFGKM classification, the H-R diagram, parallax and the parsec, and the analysis of variable-star light curves including the use of Cepheids as standard candles.

   Outcome

   the student can apply the magnitude scale and distance modulus, account for what stellar spectra reveal, classify by OBAFGKM spectral type, sketch a labelled Hertzsprung-Russell diagram and locate the main populations, account for low-mass and high-mass stellar life cycles upon it, determine distances by parallax (d = 1/p) and by spectroscopic parallax, and analyse the light curves of all required variable star families. *(Edexcel 1AS0 Paper 2 — Topic 13, spec points 13.1–13.19)*

   Sub-units

   1. ○ 13.1 Apparent and absolute magnitude; the distance modulus Open this unit → ✓ ↻
   2. ○ 13.2 Stellar spectra: composition, temperature, radial velocity Open this unit → ✓ ↻
   3. ○ 13.3 The OBAFGKM classification scheme Open this unit → ✓ ↻
   4. ○ 13.4 The Hertzsprung-Russell diagram and stellar life cycles Open this unit → ✓ ↻
   5. ○ 13.5 Inverse-square law, the parsec, and heliocentric parallax Open this unit → ✓ ↻
   6. ○ 13.6 Spectroscopic parallax via the H-R diagram Open this unit → ✓ ↻
   7. ○ 13.7 Variable stars: eclipsing binaries, Cepheids, novae, supernovae Open this unit → ✓ ↻
   8. ○ 13.8 Cepheids as standard candles Open this unit → ✓ ↻
   9. ○ 13.9 Cepheid Period-Luminosity as a Standard Candle Open this unit → ✓ ↻
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